Science —

307-million-year-old “monster” fossil identified at last

Scientists have figured out this mystery animal from the Carboniferous.

Reconstruction of the Tully Monster as it would have looked 300 million years ago, swimming in the Carboniferous seas. Notice the jointed proboscis, the multiple rows of teeth, and the dorsal eye bar.

Sean McMahon

The "Tully monster," a mysterious animal that swam in the inland oceans of Illinois more than 300 million years ago, left behind a tantalizingly detailed map of its body in a well-preserved package of fossils. Unfortunately, nobody could figure out what the creature was for half a century—until now.

Francis Tully found the remains of the tiny beast (it's only about 10 centimeters long) in Illinois in 1958 and gave it the whimsical scientific name Tullimonstrum (nickname: Tully monster). A long stalk extends from the front of its body, which ends in a toothy orifice called a buccal apparatus. Its body is covered in gills and narrows down into a powerful tail that it probably used for propulsion. Its eyes peer out from either end of a long, rigid bar attached to the animal's back.

The Tully monster lived during the Carboniferous period, when the North American Great Basin was an enormous inland sea. Trees were colonizing the land for the first time, transforming the soil and filling the atmosphere with higher levels of oxygen than Earth had known before or since. Giant arthropods, like the 8-foot-long millipede known as Arthropleura, crawled through the new forests. It was a good time to be a weird animal, and the Tully monster probably fit right in.

But where did Tullimonstrum fit into the history of life in the seas? A team of researchers has just published a paper in Nature explaining its likely lineage. They analyzed the fossils using scanning electron microscopes, which allowed them to explore the anatomy of the Tully monster inside and out. To their surprise, they discovered that the animal appeared to have a backbone. Previously, scientists had toyed with the idea that it might be an invertebrate related to today's snails. The hints of a skeleton, combined with the structure of the animal's gut and mouth, revealed parallels with today's hagfish and lampreys. Like hagfish and lampreys, Tullimonstrum has a jawless mouth lined with teeth.

"The buccal apparatus of Tullimonstrum suggests that it grasped food with its bifurcate anterior projection and rasped pieces off with the lingual apparatus," the authors conclude. Which is to say, the Tully monster used that long, toothy protrusion from the front of its body to grab food, and then it ripped bites off using a long, powerful tongue. And it needed that weird-ass eye arrangement to see what it was doing at the end of its mouth proboscis. Once again, science has helped us understand the origins of nightmare fuel in evolutionary history.